Endosymbiosis

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to squeeze the lachrymal gland. This produces tears that flow too fast to be drained away. The eyelashes catch many flying particles that otherwise would enter the eye. As further protection, the eyelids automatically close when an object suddenly moves close to the eye.

The eye is made of 3 coats, or tunics. The outermost coat consists of the cornea and the sclera. The middle coat contains the main blood supply to the eye and consists of the choroid, the ciliary body, and the Iris. The innermost layer is the retina.

The Sclera, or the white of the eye, is composed of tough fibrous tissue. On the exposed area of the eye the scleral surface is covered with a mucous membrane called the conjunctiva. This protects the eye from becoming dry.

The Cornea, a part of the sclera, is the transparent window of the eye through which light passes. The focusing of the light begins in the cornea. Behind the Cornea is a watery fluid called the aqueous humor. This fluid fills a ...

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nutrients to the eye. The ciliary body is a muscular structure that changes the shape of the lens.


Behind the pupil and iris are the crystalline lens and the ciliary muscle. The muscle holds the lens in place and changes its shape. The lens is a colorless, nearly transparent double convex structure, similar to an ordinary magnifying glass. Its only function is to focus light rays onto the retina. The lens is made of elongated cells that have no blood supply. These cells obtain nutrients from the surrounding fluids - the aqueous humor in front and the vitreous body, a clear jelly, behind.

The shape of the lens - essentially that of a flattened globe - can be changed by the ...

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